Problem: In geometry class, the girl to boy ratio is $8$ to $10$. If there are a total of $90$ students, how many boys are there?
Explanation: A ratio of $8$ girls to $10$ boys means that a set of $18$ students will have $8$ girls and $10$ boys. A class of $90$ students has $5$ sets of $18$ students. Because we know that there are $10$ boys in each set of $18$ students, the class must have $5$ groups of $10$ boys each. There is a total of $50$ boys in geometry class.